Another thing that I have found has worked is to open the .m3u file in notepad. When you do, it will look something like this:
#EXTM3U
#EXTINF:*, Artist - Album
..\other folders in here\Music\Artist\Album\Song Title.mp3

What you need to do is delete the folders between \Music and the .. You can do this by clicking the Edit menu and then going to Replace. After you do that, enter the folders between \Music and .. and replace it with nothing. After you do this you can copy the revised .m3u files to the playlists folder on the J3. Your playlists will then work as long as all of the music files in the playlist are on either the internal or external storage depending upon where you placed the playlist file. In other words, just keep your songs on the same drive that you put the playlist. Then everything will work.